IE9 jqXHR.responseXML returns "undefined"

IE9 jqXHR.responseXML returns "undefined" while FireFox 3.6.13 correctly returns: [object XMLDocument]

HTML

<html>
    <head>
        <meta http-equiv="content-type" content="text/html; charset=utf-16"/>
        <title>Hello</title>
    </head>
    <body>
    </body>
</html>

JavaScript

//
// we have to post to /echo/xml/ the data we want it to return
$.ajax({
    url: "/echo/xml/",
    type: "post",
    data: 'xml=<?xml version="1.0" encoding="utf-8"?><hello><world>earth</world></hello>',
    dataType: "xml",
    success: function(data) {
        console.log(data);
    },
    complete: function(xhr, status) {
        $("body").html(xhr.responseXML);
        console.log(xhr.responseXML.childNodes.length);
    }
});

// please run on ie9 rc